1. Field of the Invention
The present invention relates to a fuel injector for an internal-combustion engine. In particular, the invention relates to an injector comprising a casing, fixed on which is a nebulizer having a nozzle for the fuel under pressure, an axially mobile needle for opening and closing the nozzle by means of a first end thereof, and a rod for controlling the needle, which is controlled by the fuel under pressure, aided by a compression spring.
2. Description of the Related Art
As is known, the control rod is substantially coaxial with the needle, which is normally pushed into a closing position of the nozzle by the fuel under pressure in a control chamber, associated to a metering solenoid valve. The compression spring is set in a cavity of the casing and acts on the needle in general through a washer or other element for adjustment of the lift of the needle and/or of the pre-loading of the spring. Furthermore, in general, set between the rod and the needle is an intermediate element, which is provided in classes, such as to enable adjustment of the total axial dimensions of the ensemble formed by the needle, the intermediate element and the rod. The intermediate element presents the drawback of generally causing a certain transverse component of the action of the rod on the needle, which leads to an irregular wear and hence a faster deterioration of the injector. In order to limit this drawback, generally the intermediate element must be made with very high precision, which consequently renders it relatively costly and complex to provide.
In a known injector, the needle has a second end having a conical depression, on which the rod acts. In order to guarantee a perfectly axial resultant of the mutual action of the second end of the needle by the rod, the conical depression of the needle is engaged through an intermediate ball. In a variant of this injector, the conical depression of the needle is engaged directly by one end of the rod, which is shaped so as to guarantee a perfectly axial resultant of the mutual action. This known injector is relatively costly to produce, also on account of the conformation of the two engagement ends and of the shims for the spring.